Transcript Document

Exercise capacity following heart transplant: case report on the physical work
capacity of a 37 year old competitive cyclist following orthotopic heart transplant
*William F. Goodman PA-S, **Kenneth H. Pitetti PhD., ***Jeremy Patterson PhD., Hussam Farhoud M.D.
*Department of Physician Assistant, College of Health Professions, **Department of Physical Therapy, College of Health Professions, ***Department of Kinesiology and Sport Studies, College of Education
INTRODUCTION
RESULTS
The great majority of heart transplant recipients (HTRs), because of end-stage heart
failure, experience a slow decline in physical work capacity (PWC; Watts and/or peak
oxygen uptake, VO2peak Ml•kg-1•min-1) prior to surgery (i.e., < 60% peak-predicted
VO2peak).[1] Studies comparing PWC before and soon after transplantation (~2 months)
have shown significant (+ ~ 30% of pre-transplant value) spontaneous recovery of
PWC.[1] However, post-transplantation PWC of HTRs normally does not exceed 60% of
the value for healthy age-match controls.[2]
At the time of the post-transplant PWC evaluation, neither left ventricular dysfunction
(i.e., cardiac allograft vasculopathy, oxidative stress, and/or activation of various alloantigen-dependent and –independent factors caused by cytokine release) nor lung
limitations (i.e., diffusion abnormalities) had been detected by his medical team. This
suggests, for the participant in this report, that chronotropic incompetence (i.e., central)
and muscle limitations (i.e., peripheral) would remain as the major limitations to his PWC
following transplantation.
This paper presents the case of a 37 year-old, professionally trained cyclist who
suffered a cardiovascular event immediately following a road race of 52 miles and
ultimately received a heart transplant four months following the event. Two months prior
to the cardiovascular event the participant completed a PWC evaluation. The participant
resumed training one month following surgery and underwent an exercise stress test six
months post surgery. The focus of this report is threefold: 1) comparison of PWC prior to
acute myocardial infarction (AMI) to PWC following heart transplant; 2) level of PWC
following surgery in comparison to age-matched HTR peers; and 3) ability/limitations to
resume training and frequency and intensity of that training.
Table 1. Cardiopulmonary Exercise Test results 6 months post transplant.
Resting
Max Achieved
Predicted
% Predicted
VO2max (ml•kg-1•min-1)
15.1
33.8
36.7
92.2
VO2 (ml•kg-1•min-1)
1479
3316
3606
92
RER
0.95
1.18
VE (l/min)
42.87
133.32
VE/VO2 (L/L)
41.08
VE/VCO2 (L/L)
34.73
Freq (br•min-1)
26
63
VT (ml•min-1)
1666
2899
HR (bpm)
115
165
Workload (W)
25
250
183*
90
*determined from 220 – age (actual HRmax determined by testing prior to AMI was 171 bpm). VO2max, maximal oxygen uptake; VE/VO2, ventilatory equivalent
from oxygen; VE/VCO2, ventilatory equivalent from carbon dioxide; RER, respiratory exchange ratio; VT, ventilatory threshold; Freq, frequency or rate of respiration;
VE, minute ventilation
The participant underwent an orthotopic heart transplant resulting in complete
denervation of his heart. The loss in autonomic innervation of the SA node has been
reported to reduce peak heart rate (HR) response, during an incremental exercise test to
voluntary exhaustion, by 30-40% than that of age-matched controls.[2] Studies examining
responses to progressive exercise in HTR suggest that peak HR is significantly higher in
healthy controls compared to HTR (~66% of predicted) and that PWC is related to HR at
peak exercise.[3] Interestingly, results of the post-transplant exercise test show that the
participant has a good relationship between HR and the increasing workload (Figure 1). In
addition, his maximal HR achieved (165 b/min) was 90% of his maximal HR (183 b/min)
achieved during the performance test approximately one year prior to the cardiac event.
DISCUSSION
Figure 1. Heart rate response to work load. Units for heart rate are beats per minute and units for power are Watts.
METHODS
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Heart Rate
The PhysioDyne Instrument metabolic cart with Max II oxygen analyzers
(#Pm1111E) and carbon dioxide analyzer (#1r1507) were used to measure metabolic
responses in 20s averages. Peak respiratory parameters were oxygen consumption
(VO2 ml•min-1, and ml•kg-1•min-1), ventilation (VE L•min-1), and respiratory gas
exchange (RER; VCO2•VO2-1). The highest physiological parameters reached during
the final stage were considered peak performance. Heart rate (HR) was monitored by a
12-lead electrocardiograph (Marquette, USA) and recorded every minute and at peak
capacity.
Blood pressure was measured by a physician, using a mercury
sphygmomanometer, before testing, during (every 3 minutes) the test, and several times
during recovery. The gas analyzers and flow meters were calibrated according to the
manufacturer’s recommendation before and immediately after the test.
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Muscle atrophy and deconditioning are another characteristic which limits PWC in
patients immediately following HT.[5] In this study, the measured VO2max did not seem
to be limited by the participant’s muscular endurance. Although the participant achieved
92% of his predicted VO2max, the exercise data indicates that his ventilatory capacity
was limited. VE (133.32 L/min) and ventilatory equivalents for oxygen (VE/VO2) and
carbon dioxide (VE/VCO2) showed higher ratios due to inferior lung function and RER
values increased rapidly (Table 1). This may suggest that the participant’s peak exercise
capacity was limited by cardiopulmonary factors (i.e., central) rather than muscular
endurance (peripheral).
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A continual bicycle ergometer test protocol was performed on an electrically braked
cycle ergometer (Ergomed, Siemens, Erlangen, Germany). Following a 15-min warm-up
at 25-75 W, the participant started at an initial workload of 100W, then increased 25 W
every 3 minutes until volitional exhaustion.
In a comparative study, Richard and colleagues (1999) measured PWC in 14
endurance trained orthotopic HTRs.[4] Peak exercise responses for the participant in
the present study and in those reported by Richard et al. (1999) were similar for peak
heart rate ( 165 bpm vs. 159 ± 16 bpm) and VO2peak (33.8 ml•kg-1•min-1 vs. 32.5 ± 7.8
ml•kg-1•min-1), respectively. In addition, those participants had been training regularly
for 36 ± 24 months prior to testing and PWC evaluations occurred 43 ± 12 months
following heart transplant (HT). In comparison, the participant in this study had been
cleared from all training restrictions three months prior to PWC evaluation which took
place 6 months following HT.
25
0
50
100
150
Pow er (W)
200
250
300
This ventilatory limitation is similarly found in lung transplant recipients where the
adaptation of the respiratory system is slower to catch up to the cardiovascular
system.[6] This suggests that the deconditioning that occurred in the pulmonary
system between the time of cardiovascular (CV) event and HT is a significant factor in
reconditioning and may need to be the focus of HT rehabilitation.
CONCLUSION
In this case study, several months of high volume endurance training immediately
following HT showed significant improvement in aerobic capacity and work load.
Although this is an unusual case study, it is clear that physical activity immediately
following HT and adherence to an individualized program that promotes an active life
style helps to restore CV function. These results suggest that a more aggressive
approach to HT recovery should be studied.